A genetic marker for noveltysensationseeking behaviour

In January 1996 two independent teams reported that a particular chromosomal 'locus' was associated with a well-established trait of human temperament—the hunger for novelty and excitement that lies behind impulsivity or sensation-seeking behaviour. (1.I and 29 A polymorphism in the sequence of the gene expressing the D4 dopamine receptor (D4DR), located on the short arm of chromosome 11, explained 10 per cent of the genetic variance due to this trait. Individuals with the longer repeat allele at exon III of the D4DR gene scored higher in novelty-seeking behaviour (explorers, risk-seekers), whereas those with the shorter allele had lower scores (prudent, cautious). The first of these studies(1.9) investigated a heterogeneous sample of young Israelis, and showed the association to be independent of ethnicity (Ashkenazim versus Sephardim), sex, or age. The second study, carried out in the United States, (29 used a random sample of people who had initially been recruited in a search for chromosomal regions possibly associated with sexual orientation; this sample mainly comprised white men, although some ethnic minorities were also included. The personality questionnaires used in the two studies were also different: the Israelis were evaluated using Cloninger's Tridimensional Personality Questionnaire (TPQ),(21> which gives direct scores of novelty-seeking behaviour, whereas the American study used the Revised NEO Personality Inventory (22> which measures the five superfactors mentioned above, from which scores for novelty-seeking were derived. The results of the two studies were highly concordant. The American sample had the additional advantage of including intra- and extrafamilial comparisons as the sample contained many pairs of siblings.

Despite the small explanatory power of this reported association, the link between temperamental variability for one trait and a chromosomal polymorphism was the first evidence for a direct relationship between a putative 'genetic marker' and a core dimension of normal personality. In this case, the potential genetic marker appeared promising because of the amount of basic clinical research linking dopaminergic function with the regulation of stimulus-seeking, sensitivity to incentives, and impulse control behaviour. In theory, if similar degrees of explained variance were assignable to other sound gene markers, a substantial part of the heritability of the trait could be explained.

Subsequent studies in Finland, (29 Sweden,(2,29 and New Zealand(26) failed to replicate these early findings. However, the heterogeneity of the samples could explain the disparate results. Although further research is required, it may be useful to remember that previous work, mostly with twins, consistently established that novelty-seeking behaviour was moderately heritable (40 to 50 per cent). In any case, it is important to reiterate that such an association, if confirmed, only accounts for part of the genetic variance in a normal dimension of temperament.

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